Impressive, perfectly straight beeches reaching up to the sky: the Sonian forest didn’t gain its nickname ‘beech cathedral’ for nothing. But global warming could change that familiar view.

74% of the Sonian Forest consists of beeches. The beech is a typical tree for a temperate climate with soft winters and plenty of rain, like our own. Or better said: like our own used to be. The last few years have seen a lot of changes in our climate. And beeches aren’t happy with those.

Decreased growth rate

Beeches are vulnerable trees. They cannot handle heat and drought very well. But the Sonian beeches are exposed to such conditions more and more frequently. The forest microclimate they live in is no longer the one they are used to, and that has its consequences. That is why Environment Brussels, along with three Belgian universities (ULB, KUL and ULG-Gembloux) and the French Agronomical Institute (Inra), studied how the beech trees in the forest are doing in 2015. This was done using dendrochronology, research using the growth rings of the beech trees. The result? Ever since 1976, the growth rate of the Sonian beeches has decreased. Beech trees love wet springs and summers that aren’t too hot, but those specific weather circumstances have been showing up less and less often since the seventies. There are more dry summers with heat waves and there is less rain in spring. In winter, there is more precipitation than before and rain showers are becoming heavier. All of this means that the beech trees no longer feel comfortable.

Is the beech tree disappearing?

Many of the beeches that form the pillars of the cathedral have been in the forest for over a hundred years. But even though beeches can grow for 500 years, they will still need to be partially replaced, preferably by species that are more resistent to changing weather circumstances. The climate forecasts for the 21st century promise little good for the beech. That is why Environment Brussels aims for a more diverse forest: winter oak, linden, hornbeam, chestnut, maple, larch, pine, … these are just a few of the species you will be able to admire in the Sonian Forest in a couple of years. Does this mean that the beech, the showpiece of the Sonian Forest, will disappear entirely? Not at all. On the one hand, it reproduces spontaneously in many places of the forest. And on the other, it is often planted in cooler spots, such as valleys or northern slopes.